Rising seas will affect major US coastal cities by 2100

February 15, 2011

This map shows where increases in sea level could affect the southern and Gulf coasts of the US. The colors indicate areas along the coast that are elevations of 1 meter or less (russet) or 6 meters or less (yellow) and have connectivity to the sea. Credit: Jeremy Weiss, University of Arizona.

Rising sea levels could threaten an average of 9 percent of the land within 180 U.S. coastal cities by 2100, according to new research led by University of Arizona scientists.

The Gulf and southern Atlantic coasts will be particularly hard hit. Miami, New Orleans, Tampa, Fla., and Virginia Beach, Va. could lose more than 10 percent of their land area by 2100.

The research is the first analysis of vulnerability to sea-level rise that includes every U.S. coastal city in the lower 48 with a population of 50,000 or more.

The latest scientific projections indicate that by 2100, the sea level will rise about 1 meter -- or even more. One meter is about 3 feet.

At the current rate of global warming, sea level is projected to continue rising after 2100 by as much as 1 meter per century.

"According to the most recent sea-level-rise science, that's where we're heading," said lead researcher Jeremy L. Weiss, a senior research specialist in the UA's department of geosciences. "Impacts from sea-level rise could be erosion, temporary flooding and permanent inundation."

The coastal municipalities the team identified had 40.5 million people living in them, according to the 2000 U.S. Census. Twenty of those cities have more than 300,000 inhabitants.

Weiss and his colleagues examined how much land area from the 180 municipalities could be affected by 1 to 6 meters of sea-level rise.

"With the current rate of greenhouse gas emissions, the projections are that the global average temperature will be 8 degrees Fahrenheit warmer than present by 2100," said Weiss, who is also a UA doctoral candidate in geosciences.

"That amount of warming will likely lock us into at least 4 to 6 meters of sea-level rise in subsequent centuries, because parts of the Greenland and Antarctic ice sheets will slowly melt away like a block of ice on the sidewalk in the summertime."

At 3 meters (almost 10 feet), on average more than 20 percent of land in those cities could be affected. Nine large cities, including Boston and New York, would have more than 10 percent of their current land area threatened. By 6 meters (about 20 feet), about one-third of the land area in U.S. coastal cities could be affected.

"Our work should help people plan with more certainty and to make decisions about what level of sea-level rise, and by implication, what level of global warming, is acceptable to their communities and neighbors," said co-author Jonathan T. Overpeck, a UA professor of geosciences and of atmospheric sciences and co-director of UA's Institute of the Environment.

This map shows where increases in sea level could affect New Orleans, Virginia Beach, Va., Miami, Tampa, Fla., New York and Washington, D.C. The colors indicate areas along the coast that are elevations of 1 meter or less (russet) or 6 meters or less (yellow) and have connectivity to the sea. Credit: Jeremy Weiss, University of Arizona.

Weiss, Overpeck and Ben Strauss of Climate Central in Princeton, N.J., will publish their paper, "Implications of Recent Sea Level Rise Science for Low-Elevation Areas in Coastal Cities of the Conterminous U.S.A.," in Climatic Change Letters. The paper is scheduled to go online this week.

Weiss and Overpeck had previously developed maps of how increases in sea level could affect the U.S. coastline. Strauss suggested adding the boundaries of municipalities to focus on how rising seas would affect coastal towns and cities.

For the detailed maps needed for the new project, the researchers turned to the National Elevation Dataset produced by the U.S. Geological Survey. The NED provides a high-resolution digital database of elevations for the entire U.S.

The high resolution let Weiss and his colleagues identify the elevation of a piece of land as small as 30 meters (about 100 feet) on a side  about the size of an average house lot.

The researchers used the USGS database to create detailed digital maps of the U.S. coast that delineate what areas could be affected by 1 meter to 6 meters of sea-level rise. The researchers also added the boundaries for all municipalities with more than 50,000 people according to the 2000 U.S. Census.

To increase the accuracy of their maps, the team included all pieces of land that had a connection to the sea and excluded low-elevation areas that had no such connection. Rising seas do not just affect oceanfront property -- water moves inland along channels, creeks, inlets and adjacent low-lying areas.

"Ours is the first national-scale data set that delineates these low-lying coastal areas for the entire lower 48 at this degree of spatial resolution," Weiss said.

The NED data set has some uncertainty, particularly for estimating elevation changes of 1 meter or less. That means the researchers' ability to identify the threat to any particular small piece of land is better for larger amounts of sea-level rise than for smaller amounts of sea-level rise, Weiss said.

"As better digital elevation models become available, we'll be using those," Weiss said. "The USGS is always improving the digital elevation models for the U.S."

Overpeck said, "The main point of our work is to give people in our coastal towns and cities more information to work with as they decide how to deal with the growing problem of sea-level rise."

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42 comments

Similar maps were published about 10 years ago predicting a 1meter rise by 2050. Even at these new slower rates of sea level rise, shouldn't we be seeing it start to happen by now? I see areas of beach front eroded by storm erosion and then relenished by local governments, but that has been going on for decades. Making predictions is great, but at some point the sea either rises or it doesn't. When does it begin?

The highest realistic estimate I have seen for 2100 sea level rise is one meter, but that is global average and that is worst case scenario. For disaster planning and long term coastal developement planning, like where to build bridges and stuff it's good to use worst case scenarios, but that should not be confused with the general consensus about what is most likely.

I could quote other sources, but most estimates come from the work of NOAA and the IPCC Working Group 1.

Climatic Change Letters is not a peer reviewed journal. It is a supplement to the journal 'climatic change' which is also not peer reviewed. It includes editorial sections and it is not required to be original work to publish in this 'journal'. This is the kind of 'journal' that you publish in when nobody good will accept your paper, or when you are just trying to pass off opinion and propaganda as science.

Warming has been occurring since the end of the ice age. The flooded shores of the ancient world can still be seen extensively on Google earth. Of course the seas are rising, they've been rising for millennia and mankind has been adapting the whole time. Today we can see ancient port cities under water that were flooded centuries before the industrial era.

Climate change is natural and ongoing. We are part of this planet's natural process and our activities are another form of its expression of life. The anti-industrial and anti-human ideology behind climate alarmism should be rejected as deceptive sham.

lol, I got down-rated because I pointed out that this pro-warming non-peer reviewed non-original work is contrary to the views of the official pro-warming government agencies who are responsible for the projections on which this article is based.

I notice that my detractors are silent on any form of rebuttal or explanation of their point of view. I suppose that is fine, as they are most likely to just resort to name-calling anyway.

This article is pure junk science. This is EXACTLY the kind of garbage that our Congress should defund in stead of making cuts to home heating assistance programs and energy subsidies.

1m is 1000mm. The sea level needs to rise 10mm a year over a full century to rise 1000mm.

Sea Level Rise is running close to zero the last 4 years and has NEVER COME CLOSE TO 10mm a year!

Why do they make this stuff up?

Where the hell did you get this misinformation?A part of europe near the coastal lines (The Netherlands) is below sea-level. We spend alot of our money preventing the sea from overcoming our dams. In the past the sea-level has risen and we have the prove of that. The only reason the sealevel did not rise much is because countries are making new rivers so that the water can go somewhere besides populated areas.

Sea level increases are already affecting some cities. Boston itself is experiencing saline infiltration and hardcore fill erosion. The rising water table's effect can be seen around almost every tower in the city.

I never said this. And the article assumes that if nothing geologically happens sea level will definitly rise. I have also stated that we made way for the water and soprobably did others that prevented the sea-level from rising much, it is part of our plan.

Sea level increases are already affecting some cities. Boston itself is experiencing saline infiltration and hardcore fill erosion. The rising water table's effect can be seen around almost every tower in the city.

Ever stepped in a mudhole. If your weight causes you to sink, it doesn't mean the water level is rising.

If you build a really heavy object like an office tower, sometimes it sinks. It doesn't mean the sea level is rising.

Much of the Back Bay and South End neighborhoods are built on reclaimed land—all of the earth from two of Boston's three original hills, the "trimount", was used as landfill material.

That land was originally a mud flat, and partially under water. No wonder you think some things are sinking when the neighborhood is built on mud.

I don't purport to speak for all Evil Climate Cranks, Paedophilic, Homophobic, Holocaust-denying, Racist climate sceptics and Flat Earthers, but this article is starting to yellow and curl at the edges, it's been pulled out of the alarmist cupboard so many times. You Warmers really need to get you act together, your ship is sinking and the world is starting a deep and steep decline into a serious cooling period and it ain't caused by CO2. The AGW/were all doomed gig is all but over, get use to it, The truth always raises to the top just like cream!

A drop in sea level for 2 of the past 5 years is a strong indicator that a changing sea level is not a great concern. In order for the IPCC prediction to be correct of a 1m increase in sea level by 2100, the rate must be almost 11 mm/yr every year for the next 89 years. Since the rate is dropping, it makes the prediction increasingly unlikely. Not even once in the past 20 years has that rate ever been achieved. The average rate of 2.7 mm/yr is only 25% of the rate needed for the IPCC prediction to be correct.

The latest comprehensive source I can find is the NOAA/CO-OPS report of 2009. Google the following: "Technical Report NOS CO-OPS 053"

Here is what they say:

global rate of sea level rise (1.7 +/- 0.5 mm/yr in the 20th century)

However, they also say the following on page 15:

None of the stations showed consistently increasing or decreasing 50-year MSL trends, although there was statistically significant multidecadal variability on the U.S. east coast with higher rates in the 1930s, 1940s and 1950s and lower rates in the 1960s and 1970s

Apparently they say that at least 50 years of good records are needed at any location in order to have a 95% confidence in +/- 0.5 accuracy. Uncertainties in land height are a problem for older records, so there isn't much of a sea level record to look at yet.

NOAA also has two different sea level scales, so be carefull which one you are looking at. One of them is actual sea level rise, while the other also includes relative changes in land elevation. That second one will show places like Miami, Boston and Dallas having much faster sea level rise than nearby areas, due to land subsidance (because they are pumping up too much ground water mainly). That scale will also show sea level around Alaska decreasing rapidly because of continental uplifting there.

Skeptic_Heritic, the salt water intrusion at Boston (and Miami and Dallas) is mainly because of ground water use, not sea level rise. They are emptying the ground reservior and sea water is seeping in to fill the void.

I should clarify my comment about emptying the ground water reservior. In fact there isn't an actual void. It's more like a sponge that's always full of water, but by pumping water out of an area they decrease the pressure there and so the pressure of salt water from one side can overpower the pressure of fresh water on the other side, which allows the salt/fresh boundary to move inland. A drought can cause this too.

Sea level around New Orleans is a non-issue. That city will sink and need to be moved eventuall, even if sea level falls. River deltas self-adjust to sea level. They fill in the low areas with silt, causing the whole region to subside. As one area fills with silt, another area will sink lower and become the new low spot. Then that area will fill with silt. Rinse and repeat. The city of New Orleans is surrounded by sinking land. They will need to do something eventually. It's a river delta. Duh.

GSwift, so exactly how does saline infiltration occur outside of ocean level systems?

I'm not sure what you are talking about, but I'll give it a stab. In a river opening, salt water will mix with the outflowing fresh water through tides and vortex mixing. That salt water can work its way quite a good distance upstream in some cases. Keep in mind that most rivers have sub-surface flow that excedes the above-ground flow. There's a lot of water exchange below the ground near the coast. Salts are also drained off the surface in runoff from roads and agriculture as well as natural sources. Pumping up ground water also tends to 'stir up' the underground aquifers and increase the salt content through mixing of water and minerals that otherwise would remain nearly stationary.

Are any of those situations possibly what you are talking about? If you are suggesting that land above sea level is getting saturated with salt water, then I'm not sure how that relates to sea level changes.

No, they're finding salt water infiltration in the foundation soils of buildings. This is of note as the pylons driven long ago to support the buildings are not being destroyed by the saline infiltration into the grounds of the city.

NOAA also has two different sea level scales, so be carefull which one you are looking at. One of them is actual sea level rise, while the other also includes relative changes in land elevation. That second one will show places like Miami, Boston and Dallas having much faster sea level rise than nearby areas, due to land subsidance (because they are pumping up too much ground water mainly). That scale will also show sea level around Alaska decreasing rapidly because of continental uplifting there.

Skeptic_Heritic, the salt water intrusion at Boston (and Miami and Dallas) is mainly because of ground water use, not sea level rise. They are emptying the ground reservior and sea water is seeping in to fill the void.

Dallas? At 775 ft., Dallas, TX is too far from the coast, and too high in the air, to be worried about sea level rises.

Disagree. He's not FoS, he just has an incomplete picture on the topic, as most of us do.

He is FOS. Has anyone read any articles about sea levels going down? Has anyone read any articles about about animals not going extinct anymore? Has anyone read any articles about people not starving anywhere anymore? Has anyone read any articles about increased levels of clean water? Has anyone read any articles about the rain forests getting bigger? Has anyone read any articles about CO2 levels going down? Has anyone read any articles about the ocean getting cleaner? We are drowning in a sea of bad news, how can these skeptic fools like Gswift not see the truth? The writing is on the wall, on the floor, on the ceiling, in the news, in the sky, on the air, it is everywhere.

Dallas? At 775 ft., Dallas, TX is too far from the coast, and too high in the air, to be worried about sea level rises

Sorry, I meant Houston. I had Dallas stuck in my head from another article I was reading. Ooops.

And Gswift is FOS.

Disagree. He's not FoS, he just has an incomplete picture on the topic, as most of us do

Okay, here's a USGS report from last Spring. This is the most comprehensive and current report I could find. This field changes so fast that anything 2 years old is out of date. Try to find the following:

ht(delete_me)tp://www.sealevelrise2010.org/Burkett, Virginia.pdf

Starting on page 22, you'll see them start talking about the things I was trying to say above. On page 27 there is a map of the US east and gulf coast with measured sea level change including land subsidance. Notice, Mobius, that I am not claiming that sea level isn't increasing, though the past 2-3 years have decreased. Support your claim about me with some evidence.

SH is correct. I have no delusions about sea level not increasing. I fully accept the fact that the Earth has warmed. Sea level will increase when the temperature increases. Duh. Short term decreases in sea level will happen from year to year as we have seen in the past couple years. That doesn't mean much though. The long trend is clearly increasing. The only significance in the recent decrease is that it may mean that assumptions about accelerating sea level change could be off. I say could, because as SH pointed out, none of us (or the scientists) can be sure at this point, though 95% confidence projections are probably pretty darn good. We're learning so much. The next 20 years will see this branch of science become much more mature.

If you are too busy to read the whole report I linked to, at least read the "key messages" on page 40. I tend to trust the USGS more than certain other sources, as they tend to be less political, compared to GISS for example. The USGS budget doesn't really hinge on climate change, so there may be less conflict of interest here.

That depends on what happens to ground level there, as well as several other factors such as erosion, as indicated by the report I linked to. The areas with the greatest risk for sea level problems will actually have problems regardless of whether the actual sea level changes or not. Relative sea level changes faster in some places than absolute sea level, because of changes in the land rather than the sea.

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